《计算机网络——自顶向下方法与Internet特色》幻灯片L-精选（公开课件）.ppt

Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 Socket programming with TCP Chapter 2: Application Layer Our goals: Conceptual and implementation aspects of network application protocols transport-layer service models client-server paradigm peer-to-peer paradigm learn about protocols by examining popular application-level protocols HTTP FTP SMTP / POP3 / IMAP DNS programming network applications socket API Some network apps E-mail Web Instant messaging Remote login P2P file sharing Multi-user network games Streaming stored video clips Internet telephone Real-time video conference Massive parallel computing Creating a network application Write programs that run on different end systems and communicate over a network. e.g., Web: Web server software communicates with browser software little software written for devices in network core network core devices do not run user application code application on end systems allows for rapid application development and propagation Chapter 2: Application layer 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 Socket programming with TCP 2.1.1 Application architectures Definition: The application architecture is designed by the application developer and dictates how the application is organized over the various end systems. There are three predominant architectures used in modern network applications: Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P 1. Client-server architecture server: always-on host (server) permanent IP address server farms (服务器集群) to create a powerful virtual server clients: communicate with server may be intermittently connected may have dynamic IP addresses do not communicate directly with each other 2. Pure P2P architecture no always-on server arbitrary end systems (Peers) directly communicate peers are intermittently connected an